"The Divine Eagle is a low observable, high altitude UAV meant [to] detect stealth aircraft at long ranges, using special purpose radars." "Formations of Divine Eagle UAVs are expected to provide an early warning line to detect threats to China's airspace, like cruise missiles and stealth bombers, as well as be able to take on such missions as hunting for aircraft carriers in the open waters of the Pacific."

"The double bodied layout was chosen in order to provide the surface area for carrying large radars, while minimizing internal volume and weight."

"This CGI offers a view of the differing yellow, green and grey blue primer coatings on the Divine Eagle suggest the usage of different materials like composite and aluminum alloys for different sections of the UAV. For example, the grey blue forward dome on the port (left) body is likely to contain a satellite dish for long distance communications, while the grey blue sections on the twin bodied fuselage likely house radar arrays."

"[The] yellow, green and grey blue primer coatings on the Divine Eagle suggest the usage of different materials like composite and aluminum alloys for different sections of the UAV. For example, the grey blue forward dome on the port (left) body is likely to contain a satellite dish for long distance communications, suggesting that the material used in the grey blue sections are likely to be highly permeable to electromagnetic waves. The grey blue is also to be found on the starboard side of the right body (facing outside), and if the airframe composition is symmetrical, likely to be found on the portside of the left body (also facing out). Such electromagnetic permeables are likely to house the Divine Eagle's long range anti-stealth radars (radomes are made of radar transparent materials), indicating that its radar arrays are 10 meters long, which suggests transmitting lower frequency (L and S Band) radar waves (most stealth aircraft are optimized to evade higher frequency, such as X band, radar). The green primer likely covers lightweight materials such as composite, while the yellow primer near the engine suggests some stronger metal alloy, probably to support the engine weight and height."

Why would China build a complex double-body aircraft instead of a single large fuselage (like the Global Hawk)?

The only scientific explanation is an interferometer.

Satellites in space (where there is no air) can fly in fix formations and perform as a single larger interferometer. An example is China's NOSS (ie. Naval Ocean Surveillance Satellite) triple satellite formation.

The problem with aircraft is air turbulence. It's difficult to maintain a fixed distance between two radar receivers.

Thus, China's Divine Eagle UAV has two long connected fuselages to serve as an interferometer that detects longer-wavelength L-band electromagnetic waves.

As a reminder, an interferometer dramatically increases the resolution (or clarity) of a returned radar signal. However, it does not affect the range of the radar. Also, an interferometer requires an atomic clock to time-stamp the two sets of images (or data) and allow post-processing algorithms to refine the picture.

More T/R modules in bulbous radomes result in a more powerful L-band AESA radar

An L-band AESA radar is based on individual transmit/receive (T/R) modules. By increasing the number of modules in the bulbous radomes, the number of constructive interference waves has been increased. This results in increased range. Another way of expressing the increased range is to say there has been an increase in the power of the radar.

The L-band radar is more powerful, because more T/R modules have been placed in the radomes of the Divine Eagle anti-stealth UAV.
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VHF wavelength starts at 1 meter and requires the length of the Divine Eagle anti-stealth UAV

Since VHF wavelength is one meter and higher, very few VHF T/R modules can be placed in the radomes. Thus, due to the constraints imposed by physics, the only place to locate a VHF AESA radar with reasonable resolution is along the length of the fuselage.

To achieve interferometry, it would require two fuselages at a fixed distance from each other. The Chinese Divine Eagle anti-stealth UAV fulfills both requirements.
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By the way, an atomic clock is a small box and could easily be carried on-board the Divine Eagle UAV.

"Rubidium clocks are the most compact method of atomic time keeping. These are commonly used on satellites."

China has 15 years of experience with airborne phased array L-band radars. We expect China's software algorithms and filters to be optimized for L-band radar interferometry.

Interior of first-generation Chinese KJ-200 AEW&C.

Interior of second-generation Chinese KJ-2000 AWACS.

Interior of third-generation Chinese ZDK-03 AEW&C.
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* Currently, no one knows the radar band of the ZDK-03 AESA radar. Since all previous Chinese AWACS and AEW&C operated in the L-band, it is logical to assume the ZDK-03 AESA radar is also in the L-band. Also, the ZDK-03 is said to be modular. Thus, the radar can be swapped out or upgraded with an L-band AESA radar.

"....Chinese KJ-2000 and KJ-200 AEW&C/AWACS radars, all operate in the L-band....

Why has the L-band been so popular? With operating wavelengths of the order of 6 to 12 inches, it permits good long range search performance with modestly sized antennas, while providing excellent weather penetration, and reasonably well behaved ground clutter environments compared to shorter wavelength bands. In airborne radar applications, L-band offers an additional economy, as a single L-band design can combine conventional primary radar functions with secondary IFF/SSR functions, thus saving considerable antenna and transmitter/receiver hardware weight, cooling and volume. The latter are alone sufficient reasons to employ this otherwise heavily congested band.

Another less frequently discussed consideration is that L-band frequencies typically sit below the design operating frequencies of stealth shaping features in many fighter aircraft and UAV designs. Shaping features such as engine inlet edges, exhaust nozzles, and other details become ineffective at controlled scattering once their size is comparable to that of the impinging radar waves. This problem is exacerbated by the skin effect in resistive and magnetic materials, which at these wavelengths often results in penetration depths incompatible with thin coatings or shallow structures.

It was therefore not surprising that during the 2000/2001 Australian media debate over the Wedgetail AEW&C aircraft, US participants were quick to vocally argue the 'counter-stealth' capability of the Wedgetail's L-band AESA radar design."

If you are not building an interferometer, the RQ-4 Global Hawk single-body design is the most efficient. Here's why.

1. Simpler construction. If you split the Global Hawk vertically down the middle (and turn it 90 degrees), you basically have the two pieces of a Divine Eagle. However, the Divine Eagle will need extra material (to seal the gaping hole) to create two fuselages. Thus, the Global Hawk minimizes construction material and makes it simpler to build a surveillance UAV.

2. Less weight. Extra fuselage material imposes a weight penalty. Also, the Divine Eagle has extra horizontal connectors to stabilize the two separate fuselage bodies. All of these extras increase construction time, material, and weight.

3. Less complexity and weight. The communication connections in a Global Hawk are optimized, because the electronics are right next to one another. In the Divine Eagle, you need to wire long fiber-optic cables for the two halves of the Divine Eagle to communicate. This imposes a penalty in complexity and weight.

4. Smaller size. The payload on a Divine Eagle can be crammed into a much smaller and sleeker Global Hawk. A unitary body construction is always preferable over a double-body design if everything else was equal.

Thus, the only conclusion is that the Divine Eagle UAV is specifically designed to optimize an important feature: interferometry.

The Chinese Divine Eagle anti-stealth UAV is willing to incur all of the penalties (for not following an RQ-4 Global Hawk design) to achieve the critically important capability of L-band radar interferometry.

According to Australia Air Power, China's KJ-2000 AWACS uses L-band radar to search for stealth aircraft.

The distance from the KJ-2000 AWACS L-band radar emitter to the target is 470km. The distance from the target to the radar receiver on the KJ-2000 AWACS is another 470km. Thus, the total distance from the KJ-2000 AWACS L-band radar emitter to the receiver is 940km.

By using the KJ-2000 AWACS with a silent listening partner in the Divine Eagle (which has an extremely sensitive L-band interferometer), the KJ-2000 AWACS can illuminate a stealth aircraft at 840km and have the Divine Eagle pick up the signal at 100km away from the target.

By figuratively separating the receiver from the KJ-2000 AWACS and moving it much further down the field, a stealth aircraft can be detected at an extreme range of 840km by the Divine Eagle anti-stealth UAV.

Divine Eagle anti-stealth UAV is a special interferometer with extended range

A normal interferometer has extreme sensitivity, but the range is unchanged. This is due to two factors. Firstly, most interferometers are passive. Radio telescopes listen passively and use interferometry to enhance the resolution. Secondly, most receivers for an interferometer are separated by large distances. For example, China's Very-Long-Baseline Interferometry (VLBI) network has radio telescopes in Beijing, Shanghai, Kunming, and Urumqi.

However, the Divine Eagle UAV interferometer is special. It has two L-band AESA transmitters/receivers that are located fairly close to one another. To construct an optimal AESA radar, the T/R (ie. transmit and receive) modules are located adjacent to one another. Nevertheless, two separate AESA transmitters that are located a few feet apart should still be able to computer-synchronize their emitted radar waves constructively to create a powerful beam.

The powerful unitary L-band beam should greatly exceed the range of a single L-band AESA transmitter. The reflection of the L-band radar target would be received normally by the two separate L-band radar receivers for interferometry.

Divine Eagle anti-stealth UAV is a special interferometer with extended range

Click to expand...

If you are putting your radar into those bulbous radomes then congratulations you would be the first ones to do that. Must be a great tech feet (probably even two left ones).

And what the hocus phocus is this VHF antenna that requires the length of the Divine Eagle. Have you guys mounted two sets of radars on this thing - One L Band and another VHF one. See the second left tech feet you guys achieved.

And what is the special interferometer you have on that thing. The world does its interferometery on a single platform, easily without the need for two separate fuselages. Are they idiots who could not figure out what was invented in the middle kingdom.

Whether you use the bus or the UAV itself as a benchmark, the height of the Divine Eagle UAV is about 1.5 meter in height.
"By using the single deck bus in the background (probably 3.2 meters tall, like most buses of its type) as a very crude visual yardstick, a very rough comparison suggests that the Divine Eagle is about 6 meters tall...."
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The radome is usually equidistant in the vertical and horizontal directions. This means the horizontal width of the Divine Eagle UAV radome is about 1.5 meters. The Divine Eagle interferometer has a diameter of 5 radomes or 7.5 meters.
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The diameter of the Divine Eagle L-band interferometer is 7.5 meters. L-band is 0.15m. However, the transmit/receive (T/R) module of an AESA radar is built with a half-wave dipole antenna design. In the case of L-band, the half-wave of 0.15m is 0.075m.

Look man, real chinese (not an imbecile like you) are intelligent enough and observant enough to not put their TR Array on that 1.5 meter radome, when they have a lot more of real estate available elsewhere.

That radome, you point out most likely there to house the communication antennas just like the Global Hawks.

My guess is that the bulges on the outer-side of both the fuselages is where the array is. Typically only one communication antenna would have sufficed but this thing seems to have two. So probably this twin fuselage air-frame is meant to allow it to work, also as a relay station (in addition to its primary purpose of housing the L band array), using more than one antenna arrays for communication.

The twin fuselage also allows for much larger fuel capacities and given the solitary engine this thing most likely was designed as a solution to the problem of producing very long endurance HALE. Which is understandable considering that the westerners can rely on far advanced engine technology to achieve the very high efficiency of fuel burn that a long endurance HALE would require. Since the Chinese like us do not have a good enough engine tech available they were wise enough to have increased the fuel fraction instead. I would also like the Indians to pursue similar designs.

Was this thing made for the PLA Navy? That is where this thing makes the most amount of sense.